Wind flow is predominantly a stream of air that moves in a direction against the general direction of the prevailing winds and is associated with a wind shear. Wind gust is one of the most dangerous weather phenomena occurring at locations where the wind direction suddenly changes. The effects of a wind shear on take-off and landing distances are multiple. In the first place, a wind shear induces downdrafts and cumulus clouds. The downdrafts increase the local lift component of the wind vector. At higher elevations, the downdrafts are usually stronger, because onset F10 (or the minimum wind velocity 10 m above the surface) is higher. To complete a given take-off, the pilot has to accelerate from a lower starting velocity to the critical take-off speed. The downdrafts slow down the entire take-off process, resulting in increased take-off distance and thus in reduced climb performance as well. A second effect is added by the effect of the downdrafts on temperature. They reduce the physical ability of the plastic foil in front of the airframe to resist the heat from friction, which increases the lateral heat load. The lateral heat load is the heat generated by friction on the airframe and the fuselage. A third effect is the drag introduced by the downdrafts and cumulus clouds. They slow down the plane and thus increase total flight distance and reduce climb performance. This is due to the the fact that downdrafts and cumulus clouds produce turbulence. The turbulence disturbs the boundary layer (layer of air contacting the surface of the airframe) and disturbs the air flow over the airframe surfaces resulting in a reduced lift coefficient (see graphic).
Aeroplane performance during take-off and landing (the transition between the runway and standard departure and arrival paths, normally to or from a height 10 m above the surface) is directly impacted by lower atmosphere temperature, pressure and the wind vector. This means that increased temperatures, reduced pressure and reduced headwind component all increase take-off and landing distances. Furthermore, increased temperature and reduced pressure (otherwise expressed: increased density altitude) result in shallower climb angles (Swatton 2008). d2c66b5586